Modern hard disc drives comprise a mechanical housing which encloses one or more rigid discs that are rotated at a constant high speed. Data are stored on the discs in a plurality of concentric circular tracks by an array of transducers ("heads") mounted to a radial actuator for movement of the heads relative to the discs.
The heads are mounted via flexures at the end of a plurality of arms that project radially outward from an actuator body. The actuator body pivots about a pivot shaft, such as a vertical post which extends upwardly from the housing. The post is parallel with the axis of rotation of the discs so that the heads move in a plane parallel with the surface of the discs.
Typically, such radial actuators employ a voice coil motor to position the heads with respect to the disc surfaces. The voice coil motor includes a magnetic circuit mounted to the disc drive housing and a coil mounted on the side of the actuator body opposite the head arms so as to be immersed in the magnetic field of the magnetic circuit. When controlled current is passed through the coil, an electromagnetic field is set up which interacts with the magnetic field of the magnetic circuit to cause the coil to move in accordance with the well-known Lorentz relationship. As the coil moves, the actuator body pivots about the post and the heads move across the disc surfaces.
In the manufacturing of a disc drive, it is important that the actuator assembly be placed in the proper location, centered on all three axes, longitudinal, latitudinal, and translational (x, y, and z) with respect to the discs. Typically, the actuator assembly has a large bored recess which accommodates a cartridge bearing assembly with a pair of ball bearing assemblies to accommodate rotation of the actuator assembly about the z-axis. The cartridge bearing assembly includes an inner bored recess to allow the actuator assembly to fit over the post. The diameters of the large bored recess and the inner recess are maintained within predetermined, close tolerance ranges.
A tolerance ring can be advantageously used to compensate for variances of the manufacturing tolerances and thus contribute to the proper positioning of the actuator assembly in all three axes. Exemplary prior art tolerance ring configurations are disclosed in U.S. Pat. No. 5,315,465 issued to Blanks, U.S. Pat. No. 4,286,894 issued to Rongley, and U.S. Pat. No. 3,838,928 issued to Blaurock et al.
As will be recognized, the continuing trend in the industry is to provide ever increasing consistency in the manufacturing of disc drives in order to promote higher performance levels in the resulting drives. However, current tolerance rings are so designed that the amount of insertion (installation) force required to overcome the compression force of the ring varies widely during the course of installation on a single drive. Such installation force ranges, or profiles, can also vary widely from drive to drive due to the range of acceptable manufacturing tolerances necessary to facilitate large scale manufacturing environments. For example, where the inner recess in a cartridge bearing assembly is at the high end of the tolerance range (i.e., having the largest allowable circumference), relatively lesser amounts of force are required to place the actuator assembly on the post as compared to a bored recess at the low end of the tolerance range.
With continued demand for improved consistency in the installation of actuator assemblies, there remains a continuing need for improvements in disc drive assembly to provide consistent low installation force of the actuator assembly. It is to such improvements that the present invention is directed.